The first centre of population developed in the mountains away from the floor of the valley. They were the areas of the farmhouses of Zoraitz (in the vicinity of the Chapel of St. Mary known as “Antio” or “La Antigua”) and Aranburu – Elgarresta. This is clearly borne out by the fact that the first ParishChurch was built in this inhabited area.
Between the end of the 15th century and the start of the 16th century the centre began to shift down into the valley (the mountain lands were insufficient for the natural growth of the population). This began in the Eizaga neighbourhood. By the middle of the 16th century the Zufiaurre area next to the river was also inhabited.
The fact that the valley was being populated prompted its inhabitants to request and be granted the building of a new ParishChurch. Work on it began in 1576 and the old ParishChurch was kept as a chapel.
The population remained stable at around 2,000 inhabitants right up until the end of the 1950s. At the beginning of the 1960s major industrial development in the town encouraged mass immigration, which caused the population to grow to 12,619 inhabitants in 1977.
As a result of the oil crisis and the industrial crisis in general from that year onwards, the trend changed and a gradual decrease in the population took place, without the rate of natural growth making up for the emigration that was going on.
The current population is 10,324 inhabitants and the household composition is as follows:
| Age | Men | Women | Total |
|---|---|---|---|
| 0-4 | 100 | 86 | 186 |
| 5-9 | 208 | 170 | 378 |
| 10-14 | 235 | 228 | 463 |
| 15-19 | 325 | 322 | 647 |
| 20-24 | 426 | 416 | 842 |
| 25-29 | 458 | 429 | 887 |
| 30-34 | 433 | 394 | 827 |
| 35-39 | 446 | 423 | 869 |
| 40-44 | 370 | 323 | 693 |
| 45-49 | 343 | 309 | 652 |
| 50-54 | 343 | 335 | 678 |
| 55-59 | 299 | 314 | 613 |
| 60-64 | 350 | 328 | 678 |
| 65-69 | 341 | 322 | 663 |
| 70-74 | 249 | 278 | 527 |
| 75-79 | 149 | 180 | 329 |
| 80-84 | 62 | 122 | 184 |
| 85-89 | 41 | 95 | 136 |
| 90-94 | 12 | 44 | 56 |
| 95-99 | 3 | 13 | 16 |
| Year | Population |
|---|---|
| 31-12-1901 | 2.000 |
| 31-12-1911 | 2.043 |
| 31-12-1921 | 2.064 |
| 31-12-1931 | 2.418 |
| 31-12-1941 | 3.237 |
| 31-12-1951 | 3.598 |
| 31-12-1961 | 7.151 |
| 31-12-1971 | 12.215 |
| 01-03-1981 | 11.798 |
| 31-12-1991 | 11.020 |
| 31-12-1992 | 10.966 |
| 31-12-1993 | 10.835 |
| 31-12-1994 | 10.737 |
| 01-05-1996 | 10.324 |